Re: Miscellany

63) Indus Valley Civilization

The Indus Valley Civilization (the Harappan Civilization or the Indus Civilization or the Indus River Valley Civilization) is one of the earliest civilizations in the world. The civilization flourished around the Indus River basin and its tributaries consisting of present day Pakistan and northwest India. In India the largest Harappan site is located in Haryana Rakhigarhi, and the second largest is in Dholavira, Gujarat. Construction of well-planned cities by using bricks, and proper drainage system are the main features of this civilization. At the time of its height, the Indus Valley Civilization geographically extended to Egypt or Mesopotamia. On the basis of archaeological research and radio carbon dating, origin of the Indus Valley Civilization lies between 3300 – 1300 BCE. Though people used to live on the banks of the Indus River before this period but it was only during a Bronze Age when they actually started living as civilized and urban societies. Harappa and Mohenjo-daro were the two prominent cities of Indus Valley Civilization.

Facts about Indus Valley Civilization

Mohenjo-daro is the largest site and Allahdino is the smallest site of the Indus Valley Civilization.

The Indus Valley Civilization had a total population of over five million. Most of its people were artisans and traders. Merchants were very wealthy and given extra political powers.

Towns were laid down in a rectangular pattern. Most of the houses were two-storey and very spacious. Town planning is a unique feature of the Indus Valley Civilization. There were well built granaries, citadels, burial grounds and bathing platforms.

The towns used to have great baths. Though the exact purpose of baths is not clear but it is believed that these might be used for religious bathing.

Brick lined sewers is another very prominent feature of the Indus Valley Civilization. Mohenjo-daro is the most prominent of all cities of the civilization with respect to sewerage system. Bricks used in construction were built in the ratio of 4:2:1 having 11 inches length, 5.5 inches width and 2.75 inches depth.

Length, mass and time was accurately measured by the people of the Indus Valley Civilization. Also the system of uniform weights and measures were developed by them.

People were familiar with certain new techniques in metallurgy. They used these techniques to produce lead, copper, tin and bronze.

Art was in its full form during the Indus Valley Civilization. At the time of excavation many bronze, copper and pottery products along with terra-cotta toys have been excavated. Steatite seals engraved with animal figures is however the most notable among all these. The most common of all animals that was used on seals was Humpless bull or unicorn.

There are three stages of Harappan Civilization which are Pre-Harappan, Harappan and Post-Harappan known as Rojde, Desalpur and Surkotada respectively

Lothal, Balakot, Suktagendor and Allahdin (Pakistan) are the cities in Harappan civilization that were the major ports of that time.

Engineering skills were at its heights and it is clear from the construction of docks especially at Lothal.

Wheels used in Haprappa were axeless.

Roads especially in Mohenjo-daro were as wide as 10.5 mt. Harappa also had wider roads having width of 30 foot.

Similarities between the Indus Valley Civilization and the Egyptian River Valley Civilization have been noticed by the scholars. First of all both the civilizations were dependent upon river system and flourished around the Indus and the Nile rivers respectively. It has also been found out that both of these civilizations had almost similar lifestyle and customs.

Limestone and steatite were the most common materials used to make stone sculpture in Harappa.

Information about rituals and beliefs of the Indus Valley Civilization is limited at present. But according to studies it is clear that people living in this civilization used to worship deities especially fertility deities. Religious activities were performed by priests. Ritualistic baths were part of Harappan Civilization. On some of the seals there are pictures of people doing meditation and sitting in a crossed legged posture.

Also there is very less information about the language used in the Indus Valley Civilization but some scholars believe its closeness to Vedic scripts.

Reason of Indus Valley Civilization decline

Major reason given by scholars regarding the decline of the Indus Valley Civilization was a shift in the course of river and natural disasters such as drought, flood etc. Also there was decline in the trade with Egypt and Mesopotamia. Some of the scholars also believe that wars with the Aryan Civilization may also be the reason of their decline.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

64) Clinometer

A clinometer or inclinometer is an instrument for measuring angles of slope (or tilt), elevation or depression of an object with respect to gravity. It is also known as a tilt indicator, tilt sensor, tilt meter, slope alert, slope gauge, gradient meter, gradiometer, level gauge, level meter, decimeter, and pitch & roll indicator. Clinometers measure both inclines (positive slopes, as seen by an observer looking upwards) and declines (negative slopes, as seen by an observer looking downward) using three different units of measure: degrees, percent, and topo. Astrolabes are inclinometers that were used for navigation and locating astronomical objects from ancient times to the Renaissance.

A clinometer is a tool that is used to measure the angle of elevation, or angle from the ground, in a right - angled triangle. You can use a clinometer to measure the height of tall things that you can't possibly reach to the top of, flag poles, buildings, trees. Follow the directions below to create your own clinometer.

You will need:

A protractor with a small hole on the center spot orPrint out of paper protractor (see below)Poster board or card board (can be from a box) to back the protractor20 cm or about 8 inches of string or strong cottonWeight - such as a metal nut, paper clips or a small piece of clayGlue and ScissorsA strawClear Tape

Directions:

If you are making a protractor, cut out the copy of the protractor.Get the piece of poster board or an empty box. Stick the paper protractor on top of the card and cut the joined pieces.Get the straw and tape it to the straight edge of your protractor that you made above.With your pen or pencil, poke a hole through the center of the protractor where it meets the straw. Push the string through the hole and tie a large knot on the other side so it won't pull through.Tie your weight to the other end of the string.

To use the clinometer:

The diagram shows what the assembled clinometer will look like when laying an a flat surface. When using it, the straw will be on the top.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

65) Wernicke-Korsakoff Syndrome (WKS)

What is Wernicke-Korsakoff syndrome (WKS)?

Wernicke-Korsakoff syndrome (WKS) is a type of brain disorder caused by a lack of vitamin B-1, or thiamine. The syndrome is actually two separate conditions that can occur at the same time, Wernicke’s disease (WD) and Korsakoff syndrome. Usually, people get the symptoms of WD first. WD is also known as Wernicke’s encephalopathy.

Symptoms of WKS may include confusion, changes to the eyes and vision, or exaggerated storytelling, among others.

Alcoholism, or chronic alcohol misuse, is the most common cause of WKS. WKS can also be linked to diet deficiencies or other medical conditions that impair the absorption of vitamin B-1.

Risk Factors

What are the risk factors for WKS?

Risk factors for WKS are related to your diet and lifestyle.

The major risk factors for developing WKS are malnourishment and chronic alcohol misuse. Other risk factors for WKS include:

inability to afford medical care and proper foodkidney dialysis, which reduces vitamin B-1 absorptionAIDS, which makes you more likely to develop conditions that lead to vitamin B-1 deficiency

Causes

What causes WKS?

The no. 1 cause of WKS is alcoholism.

The less common causes of WKS are conditions that limit nutritional absorption. Eating and nutrient absorption can be restricted by:

gastric bypass surgery, which makes it difficult to meet nutritional needs due to limited food portionsgastric cancer, which may limit the absorption of essential nutrientscolon cancer, which can result in pain that causes you to put off eatingeating disorders

Alcoholism is the no. 1 cause of WKS because people with the condition generally have a poor diet. Alcohol also prevents vitamin B-1 absorption and storage.

Symptoms

What are the symptoms of WKS?

Lesions on the brain cause WD. These lesions are the result of a vitamin B-1 deficiency.

Prominent symptoms of WD are:

double visiona drooping upper eyelid, also known as ptosisup-and-down or side-to-side eye movementsloss of muscle coordination, or ataxia, which may interfere with walkinga confused mental state, which frequently leads to combativeness or violent behavior

WD can later develop into Korsakoff’s syndrome. People who have WKS have a variety of issues relating to memory. You may experience memory loss or be unable to form new memories.

You may also have the following symptoms if you have WKS:

amnesia for events that happen after the onset of the disorderdifficulty understanding the meaning of informationdifficulty putting words into contexthallucinationsexaggerated storytelling, or confabulation

Diagnosis

How is WKS diagnosed?

Diagnosing WKS isn’t always easy.

An individual with WKS is often mentally confused. This can make communication with the doctor difficult. Your doctor may overlook the possibility of a physical disorder if you’re confused.

Signs of alcoholism

Your doctor may first check for signs of alcoholism. They may check your blood alcohol levels. Sometimes, they’ll take a liver function test to check for liver damage. Liver damage is a common sign of alcoholism.

You may also need imaging tests, which can help your doctor find any damage that’s characteristic of WKS. Diagnostic imaging tests for WKS include:

an electrocardiogram (ECG or (EKG) before and after taking vitamin B-1, which can help your doctor find abnormalitiesa CT scan to check for brain lesions related to WDan MRI scan to look for brain changes related to WDYour doctor may also use a neuropsychological test to determine the severity of any mental deficiencies.

Treatments

How is WKS treated?

WKS treatment should begin immediately. Prompt treatment may delay or stop disease progression. Treatments are also able to reverse nonpermanent brain abnormalities.

Treatment may first involve hospitalization. At the hospital, you’ll be monitored to ensure your digestive system is absorbing food properly.

The treatment for WKS may include:

vitamin B-1 given through an intravenous line (IV) in the arm or handvitamin B-1 given by moutha balanced diet to keep vitamin B-1 levels uptreatment for alcoholism

After diagnosis, your doctor will most likely give you vitamin B-1 intravenously. Fast treatment may reverse many of the neurological symptoms of WKS.

In a small number of cases, treatment of vitamin B-1 deficiency produces a negative reaction. This is more common in people with alcoholism.

Negative reactions to receiving vitamin B-1 may vary, and can include alcohol withdrawal symptoms such as insomnia, sweating, or mood swings. You may also experience hallucinations, confusion, or agitation.

Outlook

What’s the outlook for people with WKS?

The outlook for WKS is based on how far the disease has advanced.

Receiving early treatment before irreversible damage has occurred will dramatically improve your outlook.

Mortality rates are high if WKS is left untreated. Most deaths are the result of a lung infection, blood poisoning, or irreversible brain damage.

Those who receive fast treatment can see progress in:

eye problemsmuscle coordinationconfusion

Abstaining from alcohol allows continued recovery of memory and mental function.

Pevention

How can you prevent WKS?

You can prevent WKS by avoiding alcohol and eating a balanced diet rich in vitamin B-1.

Foods rich in vitamin B-1 include:

ricepeaswhole wheat breadspinachorangesmilk

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Elmer Verner McCollum was a distinguished biochemist, organic chemist, and nutritionist who studied nutrition and its effects on health and metabolism. The discoverer of vitamins A, B and D, McCollum also found the nutritional cause of rickets, a bone disease. His twenty-six years of research at the School of Hygiene and Public Health at the Johns Hopkins Medical School in Baltimore continued his earlier research and made him an authority on how diets lacking certain vitamins or trace minerals can cause diseases. He developed a biological method to analyze foods and popularized the use of rats as an extremely valuable experimental model. By modifying the rats' diets, McCollum produced animals with rickets. Because of these studies, rickets, a disease in which bones become deformed, is virtually nonexistent in developed countries. In a field of research that had few findings of importance for decades, he was instrumental in ushering in a new era.

McCollum, the fourth of five children and the first son, was born on March 3, 1879, near Fort Scott, Kansas, to Cornelius Armstrong McCollum, a farmer believed to be of Scottish descent, and Martha Catherine Kidwell McCollum, the daughter of mountain people also originally from Scotland. McCollum grew up on a farm, and as a child he was very inquisitive, a trait he had all of his life. Oddly enough for a man who would devote his life to researching nutrition and the role vitamins play in having good health, as an infant he suffered from scurvy, a nutritional disease later determined to be caused by the lack of vitamin C. He was cured when his mother fed him apple peels, which contain this vitamin. His parents understood the value of advanced education, and his mother in particular was determined that her children should receive higher education. He attended the University of Kansas in Lawrence, where as a sophomore he became interested in organic chemistry. At the end of his junior year, he was elected to membership in Sigma Xi, the honorary scientific society. He graduated with a baccalaureate degree in 1903 and a master's of arts degree a year later. McCollum continued his education at Yale University in New Haven, Connecticut, and graduated in 1906 with a doctorate in organic chemistry.

After an unsuccessful search for a position in the field of organic chemistry, McCollum began to study biochemistry. In 1907 he became an instructor in agricultural chemistry at the Wisconsin Agricultural Experimental Station and quickly rose through the academic ranks, becoming a full professor in 1913. In his early work he performed chemical analyses on the diets of dairy cattle and studied how different diets affected the cows' health and reproductive capacities. However, he thought the procedures were long and tedious in such large animals. Fortuitously, references in scientific journals about using mice in other experiments led him to develop a rat colony for his nutritional research. This was the first rat colony used in the study of nutritional aspects of disease. The rats were fed various diets, each one lacking certain substances. Their short life span quickly enabled McCollum to determine what effect the diets had. This work helped to popularize the use of rats in other experimental situations.

In 1912 McCollum noticed that rats fed a diet deficient in certain fats grew normally again when the fats were added back in. This discovery was the first of a fat-soluble nutrient, which McCollum named vitamin A. Subsequent studies have shown that vitamin A helps makes teeth and bones strong and is necessary for normal vision and healthy skin. McCollum later demonstrated that a water-soluble substance, which he called vitamin B, was also necessary for normal health. He had created the alphabetical nomenclature for vitamins.

Although pleased with his rapid rise at the Wisconsin Agricultural Experimental Station, McCollum felt somewhat restricted in his research. At this time, funds from the Rockefeller Foundation established a School of Hygiene and Public Health at Johns Hopkins Medical School in Baltimore. Highly respected among his peers, McCollum was offered a position as the first faculty member--professor of biochemistry--which he assumed in 1917. He was made emeritus professor in 1945.

A coincidence led to the discovery for which McCollum is best known: producing rickets in rats. The rats had bending, fractures, and swellings of the ends of the long bones in their legs. But McCollum did not know recognize it as rickets until John Howland, professor of pediatrics at Johns Hopkins Medical School, stopped by McCollum's office to inquire whether anyone had ever produced rickets in rats. After McCollum described his rats, he and Howland concluded the rats had rickets. The discovery threw new light on the disease. McCollum identified the missing factor in the rats' diets that resulted in rickets, which he named vitamin D. (Another researcher had discovered a different vitamin, so C was taken.) Vitamin D aids in the absorption of calcium, which is used in bones and teeth, and is found in fortified milk, fish such as tuna and sardines, dairy products, and egg yolks. It also is formed in the body when a person is exposed to sunlight. Because of this discovery, people changed their diets to include vitamin D, and now rickets is rare in most developed countries. Some of McCollum's research efforts focused on trace elements, simple substances essential to life in very small quantities. Through his research he started to isolate these substances. McCollum showed that a deficiency of calcium eventually would produce muscular spasms. Other trace elements he focused on include fluorine, zinc, and manganese.

In addition to his laboratory research, McCollum lectured widely about progress and problems in nutritional studies. In 1923 he started writing articles for the popular press in McCall's magazine. In honor of his outstanding contributions in the field of nutrition, he received many awards. He was a member of numerous national and international organizations devoted to public health, including the international committee on vitamin standards of the League of Nations in 1931, the food and nutrition board of the National Research Council starting in 1942, and the World Health Organization. In 1948 the McCollum-Pratt Institute was created at Johns Hopkins for the study of trace elements. Years after his retirement in 1946, he remained actively interested in nutrition and related health fields and published the comprehensive book A History of Nutrition in 1957. He died in Baltimore, Maryland, November 15, 1967.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

67) Hypermnesia

Hypermnesia defines great memory capacity. This capacity is often judged as a gift by others, yet considered a pathology by the medical field. This case occurs in the context of a great improvement in episodic memory. In cases of emotional hypermnesia, memories of traumatic events of life such as war or deportation continually resurface (Targowla's syndrome). It is advisable, however, not to classify an exceptional photographic or eidetic memory as hypermnesia, since these are not pathologies but rare abilities to memorize stimuli.

Hypermnesia is an improvement in memory that occurs with related attempts to retrieve previously encoded material. Hypermnesia is the net result of reminiscence and forgetting, such that the amount of reminiscence must exceed the amount of forgetting resulting in a net improvement overall. Ballard was the first to observe hypermnesia using a multiple recall task in 1913, the same task with which he discovered reminiscence. After asking young school children to memorize poetry, he initially retested their recall abilities 2 days later only to discover that the class improved by 10 percent over the initial recall level.

Hypermnesia was not considered a phenomenon until the mid-1970s when Erdelyi and his associates completed further testing. Two suggestions have been offered to explain the increases in net recall over testing. One suggestion is that pictures and high imagery words enhance hypermnesia, speculating that this nature of stimuli is more recognizable and hence less susceptible to forgetting. The second suggestion is Roediger's level of recall hypothesis claiming that any variable that produces greater levels of depth processing lead to greater hypermnesia.

A 1991 study by Otani and Hodge suggests that hypermnesia does not occur with recognition but is found in cued recall experiments, showing that the improvement in memory performance is due to an increased rate of item recovery facilitated by relational processing. Relational processing can be made easier with well-categorized stimuli and helps to increase the availability or retrieval cues that in turn help to generate the to-be-remembered items. The phenomenon of hypermnesia is one that continues to be examined, particularly in terms of its generalization.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

68) Virus

Virus, an infectious agent of small size and simple composition that can multiply only in living cells of animals, plants, or bacteria. The name is from a Latin word meaning “slimy liquid” or “poison.”

The earliest indications of the biological nature of viruses came from studies in 1892 by the Russian scientist Dmitry I. Ivanovsky and in 1898 by the Dutch scientist Martinus W. Beijerinck. Beijerinck first surmised that the virus under study was a new kind of infectious agent, which he designated contagium vivum fluidum, meaning that it was a live, reproducing organism that differed from other organisms. Both of these investigators found that a disease of tobacco plants could be transmitted by an agent, later called tobacco mosaic virus, passing through a minute filter that would not allow the passage of bacteria. This virus and those subsequently isolated would not grow on an artificial medium and were not visible under the light microscope. In independent studies in 1915 by the British investigator Frederick W. Twort and in 1917 by the French Canadian scientist Félix H. d’Hérelle, lesions in cultures of bacteria were discovered and attributed to an agent called bacteriophage (“eater of bacteria”), now known to be viruses that specifically infect bacteria.

The unique nature of these organisms meant that new methods and alternative models had to be developed to study and classify them. The study of viruses confined exclusively or largely to humans, however, posed the formidable problem of finding a susceptible animal host. In 1933 the British investigators Wilson Smith, Christopher H. Andrewes, and Patrick P. Laidlaw were able to transmit influenza to ferrets, and the influenza virus was subsequently adapted to mice. In 1941 the American scientist George K. Hirst found that influenza virus grown in tissues of the chicken embryo could be detected by its capacity to agglutinate (draw together) red blood cells.

A significant advance was made by the American scientists John Enders, Thomas Weller, and Frederick Robbins, who in 1949 developed the technique of culturing cells on glass surfaces; cells could then be infected with the viruses that cause polio (poliovirus) and other diseases. (Until this time, the poliovirus could be grown only in the brains of chimpanzees or the spinal cords of monkeys.) Culturing cells on glass surfaces opened the way for diseases caused by viruses to be identified by their effects on cells (cytopathogenic effect) and by the presence of antibodies to them in the blood. Cell culture then led to the development and production of vaccines (preparations used to elicit immunity against a disease) such as the poliovirus vaccine.

Scientists were soon able to detect the number of bacterial viruses in a culture vessel by measuring their ability to break apart (lyse) adjoining bacteria in an area of bacteria (lawn) overlaid with an inert gelatinous substance called agar—viral action that resulted in a clearing, or “plaque.” The American scientist Renato Dulbecco in 1952 applied this technique to measuring the number of animal viruses that could produce plaques in layers of adjoining animal cells overlaid with agar. In the 1940s the development of the electron microscope permitted individual virus particles to be seen for the first time, leading to the classification of viruses and giving insight into their structure.

Advancements that have been made in chemistry, physics, and molecular biology since the 1960s have revolutionized the study of viruses. For example, electrophoresis on gel substrates gave a deeper understanding of the protein and nucleic acid composition of viruses. More-sophisticated immunologic procedures, including the use of monoclonal antibodies directed to specific antigenic sites on proteins, gave a better insight into the structure and function of viral proteins. The progress made in the physics of crystals that could be studied by X-ray diffraction provided the high resolution required to discover the basic structure of minute viruses. Applications of new knowledge about cell biology and biochemistry helped to determine how viruses use their host cells for synthesizing viral nucleic acids and proteins.

The revolution that took place in the field of molecular biology allowed the genetic information encoded in nucleic acids of viruses—which enables viruses to reproduce, synthesize unique proteins, and alter cellular functions—to be studied. In fact, the chemical and physical simplicity of viruses has made them an incisive experimental tool for probing the molecular events involved in certain life processes. Their potential ecological significance was realized in the early 21st century, following the discovery of giant viruses in aquatic environments in different parts of the world.

Definition

Viruses occupy a special taxonomic position: they are not plants, animals, or prokaryotic bacteria (single-cell organisms without defined nuclei), and they are generally placed in their own kingdom. In fact, viruses should not even be considered organisms, in the strictest sense, because they are not free-living; i.e., they cannot reproduce and carry on metabolic processes without a host cell.

All true viruses contain nucleic acid—either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid)—and protein. The nucleic acid encodes the genetic information unique for each virus. The infective, extracellular (outside the cell) form of a virus is called the virion. It contains at least one unique protein synthesized by specific genes in the nucleic acid of that virus. In virtually all viruses, at least one of these proteins forms a shell (called a capsid) around the nucleic acid. Certain viruses also have other proteins internal to the capsid; some of these proteins act as enzymes, often during the synthesis of viral nucleic acids. Viroids (meaning “viruslike”) are disease-causing organisms that contain only nucleic acid and have no structural proteins. Other viruslike particles called prions are composed primarily of a protein tightly complexed with a small nucleic acid molecule. Prions are very resistant to inactivation and appear to cause degenerative brain disease in mammals, including humans.

Viruses are quintessential parasites; they depend on the host cell for almost all of their life-sustaining functions. Unlike true organisms, viruses cannot synthesize proteins, because they lack ribosomes (cell organelles) for the translation of viral messenger RNA (mRNA; a complementary copy of the nucleic acid of the nucleus that associates with ribosomes and directs protein synthesis) into proteins. Viruses must use the ribosomes of their host cells to translate viral mRNA into viral proteins.

Viruses are also energy parasites; unlike cells, they cannot generate or store energy in the form of adenosine triphosphate (ATP). The virus derives energy, as well as all other metabolic functions, from the host cell. The invading virus uses the nucleotides and amino acids of the host cell to synthesize its nucleic acids and proteins, respectively. Some viruses use the lipids and sugar chains of the host cell to form their membranes and glycoproteins (proteins linked to short polymers consisting of several sugars).

The true infectious part of any virus is its nucleic acid, either DNA or RNA but never both. In many viruses, but not all, the nucleic acid alone, stripped of its capsid, can infect (transfect) cells, although considerably less efficiently than can the intact virions.

The virion capsid has three functions: (1) to protect the viral nucleic acid from digestion by certain enzymes (nucleases), (2) to furnish sites on its surface that recognize and attach (adsorb) the virion to receptors on the surface of the host cell, and, in some viruses, (3) to provide proteins that form part of a specialized component that enables the virion to penetrate through the cell surface membrane or, in special cases, to inject the infectious nucleic acid into the interior of the host cell.

Host range and distribution

Logic originally dictated that viruses be identified on the basis of the host they infect. This is justified in many cases but not in others, and the host range and distribution of viruses are only one criterion for their classification. It is still traditional to divide viruses into three categories: those that infect animals, plants, or bacteria.

Virtually all plant viruses are transmitted by insects or other organisms (vectors) that feed on plants. The hosts of animal viruses vary from protozoans (single-celled animal organisms) to humans. Many viruses infect either invertebrate animals or vertebrates, and some infect both. Certain viruses that cause serious diseases of animals and humans are carried by arthropods. These vector-borne viruses multiply in both the invertebrate vector and the vertebrate host.

Certain viruses are limited in their host range to the various orders of vertebrates. Some viruses appear to be adapted for growth only in ectothermic vertebrates (animals commonly referred to as cold-blooded, such as fishes and reptiles), possibly because they can reproduce only at low temperatures. Other viruses are limited in their host range to endothermic vertebrates (animals commonly referred to as warm-blooded, such as mammals).

Size and shape

The amount and arrangement of the proteins and nucleic acid of viruses determine their size and shape. The nucleic acid and proteins of each class of viruses assemble themselves into a structure called a nucleoprotein, or nucleocapsid. Some viruses have more than one layer of protein surrounding the nucleic acid; still others have a lipoprotein membrane (called an envelope), derived from the membrane of the host cell, that surrounds the nucleocapsid core. Penetrating the membrane are additional proteins that determine the specificity of the virus to host cells. The protein and nucleic acid constituents have properties unique for each class of virus; when assembled, they determine the size and shape of the virus for that specific class. The genomes of Mimiviruses and Pandoraviruses, which are some of the largest known viruses, range from 1 to 2.5 Mb (1 Mb = 1,000,000 base pairs of DNA).

Most viruses vary in diameter from 20 nanometres (nm; 0.0000008 inch) to 250–400 nm; the largest, however, measure about 500 nm in diameter and are about 700–1,000 nm in length. Only the largest and most complex viruses can be seen under the light microscope at the highest resolution. Any determination of the size of a virus also must take into account its shape, since different classes of viruses have distinctive shapes.

Shapes of viruses are predominantly of two kinds: rods, or filaments, so called because of the linear array of the nucleic acid and the protein subunits; and spheres, which are actually 20-sided (icosahedral) polygons. Most plant viruses are small and are either filaments or polygons, as are many bacterial viruses. The larger and more-complex bacteriophages, however, contain as their genetic information double-stranded DNA and combine both filamentous and polygonal shapes. The classic T4 bacteriophage is composed of a polygonal head, which contains the DNA genome and a special-function rod-shaped tail of long fibres. Structures such as these are unique to the bacteriophages.

Animal viruses exhibit extreme variation in size and shape. The smallest animal viruses belong to the families Parvoviridae and Picornaviridae and measure about 20 nm and about 30 nm in diameter, respectively. Viruses of these two families are icosahedrons and contain nucleic acids with limited genetic information. Viruses of the family Poxviridae are about 250 to 400 nm in their longest dimension, and they are neither polygons nor filaments. Poxviruses are structurally more complex than simple bacteria, despite their close resemblance. Animal viruses that have rod-shaped (helical) nucleocapsids are those enclosed in an envelope; these viruses are found in the families Paramyxoviridae, Orthomyxoviridae, Coronaviridae, and Rhabdoviridae. Not all enveloped viruses contain helical nucleocapsids, however; those of the families Herpesviridae, Retroviridae, and Togaviridae have polygonal nucleocapsids. Most enveloped viruses appear to be spherical, although the rhabdoviruses are elongated cylinders.

The criteria used for classifying viruses into families and genera are primarily based on three structural considerations: (1) the type and size of their nucleic acid, (2) the shape and size of the capsids, and (3) the presence of a lipid envelope, derived from the host cell, surrounding the viral nucleocapsid.

The nucleic acid

As is true in all forms of life, the nucleic acid of each virus encodes the genetic information for the synthesis of all proteins. In almost all free-living organisms, the genetic information is in the form of double-stranded DNA arranged as a spiral lattice joined at the bases along the length of the molecule (a double helix). In viruses, however, genetic information can come in a variety of forms, including single-stranded or double-stranded DNA or RNA.

The nucleic acids of virions are arranged into genomes. All double-stranded DNA viruses consist of a single large molecule, whereas most double-stranded RNA viruses have segmented genomes, with each segment usually representing a single gene that encodes the information for synthesizing a single protein. Viruses with single-stranded genomic DNA are usually small, with limited genetic information. Some single-stranded DNA viruses are composed of two populations of virions, each consisting of complementary single-stranded DNA of polarity opposite to that of the other.

The virions of most plant viruses and many animal and bacterial viruses are composed of single-stranded RNA. In most of these viruses, the genomic RNA is termed a positive strand because the genomic RNA acts as mRNA for direct synthesis (translation) of viral protein. Several large families of animal viruses, and one that includes both plant and animal viruses (the Rhabdoviridae), however, contain genomic single-stranded RNA, termed a negative strand, which is complementary to mRNA. All of these negative-strand RNA viruses have an enzyme, called an RNA-dependent RNA polymerase (transcriptase), which must first catalyze the synthesis of complementary mRNA from the virion genomic RNA before viral protein synthesis can occur. These variations in the nucleic acids of viruses form one central criterion for classification of all viruses.

A distinctive large family of single-stranded RNA viruses is called Retroviridae; the RNA of these viruses is positive, but the viruses are equipped with an enzyme, called a reverse transcriptase, that copies the single-stranded RNA to form double-stranded DNA.

The protein capsid

The protein capsid provides the second major criterion for the classification of viruses. The capsid surrounds the virus and is composed of a finite number of protein subunits known as capsomeres, which usually associate with, or are found close to, the virion nucleic acid.

There are two major classes of viruses based on the protein capsid: (1) those in which a single (or segmented) linear nucleic acid molecule with two free ends is essentially completely extended or somewhat coiled (a helix) and (2) those in which the nucleic acid, which may or may not be a covalently closed circle, is wound tightly into a condensed configuration, like a ball of yarn. These two classes of virus assume in the first case a long, extended rodlike structure and in the second case a symmetrical polygon.

By far the best-studied example of a helical rod-shaped virus is the tobacco mosaic virus, which was crystallized by Wendell Stanley in 1935. The tobacco mosaic virus contains a genome of single-stranded RNA encased by 2,130 molecules of a single protein; there are 161/3 protein molecules for each turn of the RNA helix in the ratio of three nucleotides for each protein molecule.

Under the right environmental conditions, viral RNA and protein molecules in liquid suspension will assemble themselves into a perfectly formed and fully infectious virus. The length of the helical virus capsid is determined by the length of the nucleic acid molecule, which is the framework for the assembly of the capsid protein. The various helical viruses have different lengths and widths, depending on the size of the nucleic acid as well as on the mass and shape of the protein molecule. Some of these helical viruses form rigid rods, while others form flexible rods, depending on the properties of the assembled proteins.

Polygonal viruses vary greatly in size, from 20 to 150 nm in diameter, essentially proportional to the size of the nucleic acid molecule coiled up inside the virion. Most, if not all, of the polygonal viruses are icosahedral; like a geodesic dome, they are formed by equilateral triangles, in this case 20. Each triangle is composed of protein subunits (capsomeres), often in the form of hexons (multiples of six) that are the building blocks of the capsid. There are 12 vertices (the apical junctions of these 20 triangles), each comprising a penton (five subunits). These icosahedral virions have three axes of fivefold, threefold, and twofold rotational symmetry. The number of capsomeres is a basis for taxonomic classification of these virus families. Certain icosahedral viruses, usually those that are more complex, contain internal proteins adhering to the nucleic acid that are not accessible at the surface of the virions.

The lipoprotein envelope

Surrounding viruses of either helical or icosahedral symmetry are lipoprotein envelopes, unit membranes of two lipid layers interspersed with protein molecules (lipoprotein bilayer). These viral membranes are composed of phospholipids and neutral lipids (largely cholesterol) derived from cell membranes during the process known as budding. Virtually all proteins of the cell membrane, however, are replaced by proteins of viral origin during budding. Although all the viral envelope lipids originate from the cell, their relative proportions vary from those in the cell membrane because the viral proteins select only certain lipids during budding.

Associated with the virion membrane are “integral” glycoproteins, which completely traverse the lipid bilayer, and “peripheral” matrix proteins, which line the inner surface. The glycoproteins contain regions of amino acids that, in the first step of viral infection, recognize host-cell receptors. Matrix proteins appear to function in the selection of regions of the cell membrane to be used for the viral membrane, as well as to aid the virion in entering cells.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

69) Triple point

One of the key actions in freeze drying is triple point. People are a bit confused with how this happens and why, and there is also a misconception that this is sublimation. The fact is that triple point is a stage you must achieve for the sublimation phase to start. Sublimation is the transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

Triple Point Explained:

In physics and chemistry, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium.

Triple point of water:

Scientific explanation: The single combination of pressure and temperature at which pure water, pure ice, and pure water vapour can coexist in a stable equilibrium occurs at exactly 273.16 kelvins (0.01 °C) and a pressure of 611.73 pascals (ca. 6.1173 millibars, 0.0060373057 atm).

Simply put, the triple point of water is the only temperature at which water can exist in all three states of matter; solid (ice), liquid (water), and gas (water vapour). This temperature is 0.01°C.

At that point, it is possible to change all of the substance to ice, water, or vapour by making infinitesimally small changes in pressure and temperature.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

70) The Land of Midnight Sun

The day that never ends

Like a prolonged sunset and sunrise all at once, the midnight sun colours heaven and earth in a reddish yellow light.

It’s tempting to wonder about all the sights and experiences that have been made under the midnight sun through the ages – by people living off the sea at the Lofoten and Vesterålen archipelagos, or the Sami reindeer herders of the far north.

The phenomena has at least made a lasting impression on several Norwegian artists and writers. This excerpt is from Knut Hamsuns Pan (1894): “Night was coming on again; the sun just dipped into the sea and rose again, red, refreshed, as if it had been down to drink. I could feel more strangely on those nights than anyone would believe” ...

The earth is rotating at a tilted axis relative to the sun, and during the summer months the North Pole is angled towards our star. That’s why, for several weeks, the sun never sets above the Arctic Circle.

Going there, you can live these moments yourself: Doing a whale safari, or exploring the wilderness inland, takes on a new dimension at night in the summer months, when you literally get to see the nature and wildlife in a different light.

If you’re not afraid of the sometimes chilly summer nights in the north, you could try a midnight swim – or you can pitch your tent in the wild and stay up while the sun doesn’t go down. Many sights and activities are open at night during these weeks, so you can do midnight golfing, cycling, river paddling or sea kayaking, or maybe just find a quiet spot to fish.

If you travel to the arctic islands of Svalbard, the sun doesn’t set between April and late August. Here you can do a midnight walk on a glacier or look at the reddish sky from a moving dogsled, experiencing the unique climate and nature near the North Pole.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

71) Einstein's riddle:

The situation

a) There are 5 houses in five different colors.b) In each house lives a person with a different nationality.c) These five owners drink a certain type of beverage, smoke a certain brand of cigar and keep a certain pet.d) No owners have the same pet, smoke the same brand of cigar or drink the same beverage.

The question is: Who owns the fish?

Hints

i) the Brit lives in the red houseii) the Swede keeps dogs as petsiii) the Dane drinks teaiv) the green house is on the left of the white housev) the green house's owner drinks coffeevi) the person who smokes Pall Mall rears birdsvii) the owner of the yellow house smokes Dunhillviii) the man living in the center house drinks milkix) the Norwegian lives in the first housex) the man who smokes blends lives next to the one who keeps catsxi) the man who keeps horses lives next to the man who smokes Dunhillxii) the owner who smokes BlueMaster drinks beerxiii) the German smokes Princexiv) the Norwegian lives next to the blue housexv) the man who smokes blend has a neighbor who drinks water

Einstein wrote this riddle last century. He said that 98% of the world could not solve it.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

Re: Miscellany

72) Four Different Types Of Teeth & Their Function

Four Different Types Of Teeth & Their Function

Teeth are perhaps the most important element found in our mouth. It plays a major role in our ability to eat as well as presentation and various other bodily tasks. In fact, if we say that healthy teeth are vital to oral health, it would not be a false statement to make. As the holder of this great gift of nature, Dr. Shervin Louie, the renowned dentist of Los Angeles, says that everyone should know and understand the what are the types of teeth human’s evolve throughout the age, their functionality, and how to take care of them. This knowledge is essential to every person who takes a keen interest in maintaining their oral health. So, let us look at the four types of main teeth and how important their functionality is to us.

Four Main Types Of Teeth

Humans have two sets of teeth from which we develop four different types of teeth throughout our life span. These two sets of teeth are:

PrimaryPermanent

Primary teeth set contains the infant or baby teeth. These teeth do not change their form until the time we grow to a more mature age in the early teens. Starting from early teens, the first of the permanent teeth starts to appear in our mouth. Once we start to develop permanent teeth, the four different types of them start to evolve as we age through the life. “These four types of teeth are about to play a major role in your life,” states Dr. Shervin Louie, a dentist in Los Angeles. Let’s learn about them now.

Incisors:

Incisors are the pair of eight teeth directly situated in the front and center of our mouth. The format includes four on top and four on the bottom. These teeth are immensely important since we use them to take the first bite of food or anything that you break with them (latter is a dangerous activity though). These teeth come in the first 6-months and then develop in a lifelong formidable shape between the ages of 6 – 8 years. Regular brushing keeps these teeth healthier and strong as well as good calcium diet.

Canines:

There are four canine teeth in our mouth and these are the sharpest of all. These teeth first appear between 11 and 20 months of age and take their lifelong formidable shape between 11 to 12 years. These teeth should stay in healthy form because they are used to tear and wear your food and plays an important part in a proper digestion process.

Like the Incisors, two are located above and two below. These teeth along with Incisors play a vital role in digestion and presentation in the form of our smile. So bad habits like smoking and chewing betel nuts severely damages them and you may end up going to a dentist in Los Angeles for a treatment. Therefore, brush daily, do flossing between the gaps of these teeth, and avoid bad habits to escape severe disease or damage.

Premolars:

Premolar teeth are situated at each side of your mouth in deep settings. These teeth are used for chewing and grinding food so that it becomes totally in a semi-liquid form helping food particles to gulp down the throat and digest smoothly. These teeth first premolar in the upper jaw appears at the age of 10 while the second in the bottom appears at 11.

Since these teeth are situated deep into the mouth and rarely gets exposure to the outside air, Dr. Shervin Louie, the renowned dentist in Los Angeles, recommends a thorough brushing and the use of mouth rinsing agents in order to protect them from bacterial attack. Also, these teeth have the most higher chances of developing plaque, tarter, and germs because of their remote location so the methods mentioned above will give them good protection.

Molars:

The final type of our teeth are the molars, a formidable replacement of permanent premolar ones. In the premolar form, there were only two teeth above and two below. However, when molars appear at the age 11 – 13 years, they add two more teeth to their pair – four above and four below –.

These molars will remain in their current form your entire life, given that you keep a good care of your dental health. As described above, molars are more prone to germ attacks and other deficiencies because of their remote location in your mouth so follow the methods of cleaning described by Dr. Shervin Louie in the paragraph above for premolars.

So, these are the major four types of teeth humans grow throughout their lifespan and their precious functionality which gives them an edge in our bodily system. As a great tip, apart from the daily care, you take off your dental health at home, it is recommended that you should at least visit twice a dentist in the 6-months period for a thorough checkup of your oral health.

It is no good to try to stop knowledge from going forward. Ignorance is never better than knowledge - Enrico Fermi.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.